Personally, focusing on whether its light or hard contact is looking at it from the wrong direction, IMO. its all relative. It has more to do with where the student is at and designing the exchange based on that, not solid absolute definitions of what makes it hard or light.

I don't teach kids, but with adults, optimal growth tends to take place just a nudge above what the student can actually handle. When youre challenged and can overcome that challenge in a short period of time, physical and psychological growth is very high, consistent, and methodical. It doesn't matter whether some sparring is classified as "hard" or "light". It should generally always feel like a slightly out of reach to provide that challenge to the student. For the instructor, it might feel light, but theyre also the one who has to control the details of the exchange. But the student should be on the edge of his seat--if a student can handle an intensity comfortably, why even waste more time at that level? Maybe a warm-up? Move on to higher intensity already...This goes for speed, level of contact, and any other variable that makes something more pressurized.

Being put WAY outside of your comfort zone has its purpose but is mostly to keep that ego in check and know you can keep going, and come out the other end alive when youre getting mauled. But that's not where you get the most improvement in your game...

I've trained in a good few different gyms given my job, so I've seen various approaches to sparring. Some like to throw you in the deep end and some would rather you gradually move up in power and contact while you gain more experience.

Personally I liked the gym that started you off with just body contact, then as you improved in skill, the instructor would decide whether or not to allow light contact to the head and legs. Then move it up in that sense. Until you can be trusted to spar withfull hard contact. Think it's a good way of transitioning into hard contact.

Also taking the approach of telling the higher belts to go easier on the lower belts until they've found their footing, though not to the extent of just standing there and absorbing shots.

Think it gives the students the feel of sparring without just getting their head kicked in. Allowing them to learn how to move against a live opponent at the early stages of training,

With this I feel you could let a student spar from day one rather than the other method I've seen where they make you wait a good few weeks before they allow you to spar.

I've trained in a good few different gyms given my job, so I've seen various approaches to sparring. Some like to throw you in the deep end and some would rather you gradually move up in power and contact while you gain more experience.

I liked the idea of calling sparring something else (we call it literally fight or practice fight). Also, the only body shots sparring is something i use with noobs mostly cause they haven't bought their mouth piss even.
We spar immediately, cause if a new comer arrives, we can't change the curriculum too much, he will work on simple techniques, but will spar with the rest, only lighter.
Thanks for your input guys.

Its really dumb to spar hard with noobs, it hurts their confidence, weeds out not only the weak but the potentially strong, it makes them ugly, it makes them not enjoy themselves, and worst of all it makes them chinny before they even start their pro career (this happened to overeem he was basically bullied and beaten up since he started off as young and small amongst older bigger boys, and this happens to many others)

I have found on multiple occasions that the worst possible thing I can do in terms of my boxing technique/skill is to spar too much and too hard with guys that are much much better than me. It makes me unsure and gunshy. It's best to work with people on my level and a little better and occasionally test myself with the real badass types. There have been a number of times when I've done very well with boxer A who is on my level, sparred a couple rounds with boxer B who is much better and then I get whipped the next time I spar boxer A again simply because I've lost faith in my offense and timing in my defense.

You can benefit from sparring hard with better partners, if you adapt. I would not concentrate on attacking, and actually "fighting" .i would concentrate on surviving with minimum of damage or points against a much better opponent. Using faints, clinches, movement etc. You fight different with different opponents. A win for you is not getting any hard punches in a round for example.
when fighting someone roughly your level, than you actually try and win.
when fighting someone less good, you try and win, but with certain techniques you need improving.

Gleason's Gm MT Trainer

Non competitive players should not hard spar at all if they are not experience. You will be directly responsible for injuries that WILL occur. Beginners gain nothing from hard sparring, they learn nothing. Hard sparring is to prepare the body to reacting to a fight pace while not losing your cool in difficult situations. Beginners do not need that and do not have the skill to avoid injuries. Weeding anyone out should be done with hard training, not hard sparring. That's just stupid.

I have to emphasise that said sparring whether hard or light is usually between two beginers.
When we pair up , size and experience dictate (usually) the pairs.
If a beginer is paired with me for example than the hard part is not practiced obviously.
About the merrits of hard sparring. I guess it depends on ones definition of a beginer. Some boxing gyms let their trainers compete from the get go. So to them it is obviously important. Also I personally think that the best lessons in boxing (like keep your hands up) are when you get punched hard. That **** resonates in your brane for a while.
I personally emphasis the benefits of light sparring on boxing and technique to my boxing partners.
Especially for begginers. If you are afraid of the punch you are less likely to try new techniques, less likely to to go toe 2 toe. Less likely to go through punches with counters etc. And the exchange is this waste of time standing outside range shooting quick solo strait punches in turns with the ocesional rabit punch panic combo. You don't box.
But if you get used to hard contact and start boxing than your advances are substantial.